The Chiefs have already stated they will not leave the area, Kansas has to be chomping at the bit to get a opportunity to get the Chiefs to move out by the racetrack and be willing to build them a new stadium with all the bells and whistles that they want. Would be just like the Jets and Giants, that play their games across the river in New Jersey.
The Royals are a totally different deal, instead of selling out 10 games, they have to sell tickets to 81 games a year, have very little walk up crowd, as its difficult to get to the games without a vehicle. While its great to go to a game there, in and out is easy, there is nothing around it for people to stay and eat before or after a game. Moving downtown would allow them to build up that area, like they have done in Atlanta and St. Louis. Atlanta's area is really great, tons of places to eat before the game, lots of condo, for young people to live and plenty of bars, all around the stadium, plus a couple of major hotels.